From PathfinderWiki

The Skittermounds are a series of tall, sandy hills which stretch for miles across the foothills of the Mindspin Mountains in the Hold of Belkzen. While they take up a large swath of land, few travelers pass through or near them, except those with few other alternatives. This is due to the complex series of ankhrav nests located within the mounds.

The warring ankhrav armies are generally content to battle each other in their leagues of underground tunnels, noticeable to those above only as a low buzzing. However, runoff from intense rain storms in the mountains floods the plain every few years, including the tunnels, which drives the ankhrav hordes from their homes to ravage the countryside in search of food while angered at the destruction of their underground realm.1

The Skittermounds were the domain of the Skittering Ravager tribe until recently. The orc tribe was destroyed in 4709 AR after an ill-fated attack on Skull Hill.2